Consumers often prefer to cook food in a microwave oven rather than conventional ovens because of the reduced cooking time required to heat foods in a microwave oven. Consumers also want to be provided with the opportunity to cook pre-packaged food products in the package in which they were purchased without the hassle of transferring the food from the package to a piece of cookware.
Unfortunately, foods cooked in a microwave oven tend to be tough and/or dry in texture and consistency, rather than tender and moist. When liquid is added to the food in an attempt to retain moisture, the food can become soggy and undesirable. In addition, microwave ovens do not evenly distribute heat to the product being cooked. This results in a cooked food product that may be very hot in one area, but cold in another area. Because of these problems, many people consider microwave cooking to be problematic and generally undesirable.
One method for improving the texture and consistency of food cooked in a microwave oven is to use steam generated by the heated food product to assist in cooking the food. Cooking with steam not only provides moisture for the food being cooked, but also results in more consistent heating throughout the food product.
Specifically, a device which uses the steam generated by the heated food product to assist in cooking the food takes advantage of the ideal gas law, a distillation of several kinetic theories including Boyle's Law and Gay-Lussac's Law. More specifically, such a device takes advantage of the proportional relationship between pressure and temperature when volume and number of gas molecules remain constant. This proportional relationship can be expressed as a mathematical equation, (P2/P1)=(T2/T1), where P1 is the initial pressure, P2 is the final pressure, T1 is the initial temperature, and T2 is the final temperature.
Accordingly, any increase in pressure will result in a proportional increase in temperature that would not occur at ambient pressures. For example, if the pressure was to increases 1.2 fold (e.g., from 1 to 1.2 atmospheres), the temperature would also increase 1.2 fold (e.g., from 275 K to 330 K, which is an increase from 35° F. to 134° F.). Such a steam cooking method is described in commonly assigned U.S. Pat. No. 6,559,431, which is incorporated herein by this reference.
In order to steam cook by this method, the volume of the device must remain substantially constant; accordingly, the device must be at least partially sealed. When a sealed device is used to heat a food product contained therein, pressure rapidly builds as steam is generated from the heated food product. As heating continues, this pressure will continue to escalate until the device's seal is broken, thereby relieving the pressure.
This relief often comes in the form of an explosion forcing the seal to open and resulting in food being ejected from the device. Not only does such an explosion create a mess, but it also undermines the attempt to use steam to cook the food product because the explosion causes a rapid release of the collected steam from the no longer sealed cooking environment.
The release of pressure can be controlled by including vents within the seal of the device, resulting in weakened portions in the seal. When the sealed cooking environment attains a pressure creating a risk of explosion, the weakened portions in the seal allow for a controlled pressure release at the vents. In addition to providing a point for the release of pressure and steam, the opening formed at the weakened portion in the seal creates one or more tabs which may be grasped and pulled, breaking the remainder of the seal such that consumption of the food product may occur. Such a venting configuration is described in commonly assigned U.S. Pat. No. 6,559,431, which has been incorporated herein by reference.
Although this type of venting configuration allows some degree of control over the location that the pressure release will occur, any one or more of the weakened portions in the seal may allow venting during a particular heating session. For example, during one heating session, two vents in a first portion of the seal may allow for pressure release while the seal remains intact at the other vents, while during another heating session, a single vent in a second portion of the seal may allow for pressure release while the seal remains intact at the other vents. Thus, the exact location and number of points at which the seal will break is difficult, if not impossible, to predict.
Furthermore, the surface area over which the seal is broken dictates how rapidly the pressure within the cooking environment will drop, thereby effecting the texture and consistency of the prepared food. Also effecting the texture and consistency of the prepared food is the location at which the seal is broken, which dictates the path of the steam being used to cook the food. Finally, since the opening formed in the seal when venting occurs creates one or more tabs which may be grasped and pulled to open the container for consumption of the food product, the location at which the seal is broken effects the convenience with which the device may be used.
Therefore, it would be desirable to provide a microwave cooking device for steam cooking which allows for improved venting control.